He is believed to be behind a series of high-profile terrorist attacks -- including the 2004 Beslan school massacre and, most recently, the attempted assassination of Ingushetian President Yunus-Bek Yevkurov.

Russia's Interfax news agency quoted an unidentified Russian law-enforcement official as saying Umarov had been killed in the operation along with four of his resistance fighters.

Chechnya's pro-Kremlin president, Ramzan Kadyrov, confirmed only that Umarov had been severely injured in the operation, which had been carried out by one of Kadyrov's commanders.

Umarov, who contacted RFE/RL by telephone from an undisclosed location in Chechnya, said he was not injured and was moving freely within Chechnya and Daghestan. He said he had just returned from a meeting of various armed groups on the border between Chechnya and Daghestan.

The resistance leader, who is the most-wanted man in Russia, said he has been collecting arms and fighters for Riyadus Salikhin, the rebel battalion founded by rebel commander Shamil Basayev, who was killed in 2006.

Units of Riyadus Salikhin carried out the Beslan siege, in which more than 320 people died, more than half of them children.

The brigade also claimed responsibility for the June 22 suicide bombing that badly wounded Yevkurov and killed one of his relatives. Increasing militant violence in the North Caucasus is seen as threatening to the Kremlin's claim that the region has been largely stabilized.

Umarov told RFE/RL that fighters under his command will attempt to avoid attacks on civilians, although he said he regards civilians as legitimate military targets.

Umarov has previously called for the formation of a North Caucasus emirate that would be ruled by Islamic law.